The purpose of this research study is to determine whether replacing the enzyme, iduronidase, which is missing in children with Mucopolysaccharidosis I (MPS I), is a safe procedure and can help slow or stop the disease. An enzyme is a type of tool used to construct the body as well as recycle and repair it. MPS children are missing an enzyme from their body and therefore, cannot recycle certain body components normally. Iduronidase, a new ivestigational product, is much like that of a normal human enzyme and should be a sufficient substitute.